code: def _boundary_symmetric(sample_coords, input_size):
      sample_coords, input_size = _param_type_and_shape(
          sample_coords, input_size
      )
      circular_size = input_size + input_size - 2
      return (input_size - 1) - tf.abs(
          (input_size - 1)
          - _boundary_circular(sample_coords, circular_size)
      )
  
file_path: NiftyNet/niftynet/layer/resampler.py
imports: from __future__ import absolute_import, division, print_function
  import tensorflow
  from niftynet.layer.base_layer import Layer
  from niftynet.layer.layer_util import infer_spatial_rank
  from niftynet.utilities.util_common import look_up_operations
label_desc: Use image node_id 3 for calling a global function with example usage: _boundary_symmetric(sample_coords, input_size) and returns: unknown